CORROSION PERFORMANCE OF PLASMA SPRAYED ALUMINA-40 wt.% TITANIA COATED HIGH-DENSITY GRAPHITE IN MOLTEN LiCl-KCl EUTECTIC SALT

The corrosion performance of plasma sprayed alumina-40 wt.% titania (A40T) coated high-density graphite was investigated in molten LiCl-KCl eutectic salt at 600 degrees C for periods of 500, 1000, and 2000 h under argon atmosphere. The microstructural and compositional investigations of corrosion-tested A40T coatings by scanning electron microscopy and energy dispersive X-ray spectroscopy showed that the samples exhibited better corrosion resistance up to 500 h. The poor corrosion behavior and failure of A40T coating from graphite substrate in the long-term (1000 and 2000 h) immersion was discussed in detail based on the microstructure and composition analysis. The phases existing in the as-sprayed coating P-Al2TiO5, gamma-Al2O3, R-TiO2, and alpha-Al2O3) remained in the detached coating after 1000 h exposure to the molten salt. The reaction between molten salt and A40T coating was not evident from XRD analysis. A40T coatings with chromium carbide-nichrome (Cr3C2-NiCr) bond coat showed complete spallation of the top coating and oxidation of the bond coat as evident from the X-ray diffraction analysis. Detachment of the A40T coating occurred due to the penetration of the molten salt into the coating through the voids and pores present on the surface, which weakened the adhesion strength between the substrate and the A40T coating or top coat-bond coat interfaces.